Transom mounted davits

[teddythetwig]

I've just come into a pair of davits for my boat, and I'm worried about the force they will exert on the transom.

The transom is perpendicular with the water, and I plan on adding a backing plate to spread the load, but the bracket is only 23 cm long and I'm wondering if there will be too much leverage. They will be supporting about 100kg of weight about a meter away from the transom.

Attached is a picture of the bracket with and without the mounting rod. The actual bracket will be a shortened version of this, so won't have as much material below the angles.

[Reefmagnet]

Hard to say, but if in doubt you can perhaps brace the davits to the stern rail. I made my own davit mounts that were similar (because I wanted to reuse the holes left from previous davits) and wasn't happy with the amount of flex in the deck (transom was fine) so added turnbuckle bracing to help stiffen things.

[coopec43]

I'm trying to understand your problem and I have come to the conclusion you have posted the picture on their side for some reason?

I do not think that bracket has any hope in hell of supporting 100 kg one meter out from the transom in a choppy sea. And I would expect the glass transom would have to be strengthened as well

The picture in the upright position is like this?

[Dockhead]

Originally Posted by teddythetwig

I've just come into a pair of davits for my boat, and I'm worried about the force they will exert on the transom.

The transom is perpendicular with the water, and I plan on adding a backing plate to spread the load, but the bracket is only 23 cm long and I'm wondering if there will be too much leverage. They will be supporting about 100kg of weight about a meter away from the transom.

Attached is a picture of the bracket with and without the mounting rod. The actual bracket will be a shortened version of this, so won't have as much material below the angles.

I think your worry is well justified. I would have an engineer look at your transom and give advice. The forces exerted are pretty huge. I think you will probably want to have some kind of reinforcement there -- some way to tie the davits into the structure of the boat.



I used to carry a large wheel steered dinghy in davits on my boat. My boat was designed for davits and has structural knees to carry the loads. But the forces were huge in a seaway and I had various problems including a davit mount breaking, davits being twisted apart, etc. etc. I don't recommend choosing a dinghy which can ONLY be carried in your davits.



After suffering with these problems for a number of years, I downsized to a folding RIB (Avon Lite 310), and smaller, manual Simpson davits, and no longer carry the dinghy in the davits on passage. I fold it down into a nice bag my sailmaker made, and lash it down on the foredeck. The folding RIB is not nearly as seaworthy as the Avon Rover 340 it replaced, and not nearly as fast, or capacious, but it's good enough for my purposes, and I am grateful every time I head out to sea with nothing in the davits to worry about. I use the davits for short trips in good weather, and to haul the dinghy out of the water overnight. Deflating and stowing in the bag is so easy and fast, reasonable even single handed, that I do this more often than I expected to.

[teddythetwig]

Originally Posted by coopec43

I'm trying to understand your problem and I have come to the conclusion you have posted the picture on their side for some reason?

I do not think that bracket has any hope in hell of supporting 100 kg one meter out from the transom in a choppy sea. And I would expect the glass transom would have to be strengthened as well

The picture in the upright position is like this?

They uploaded like that, it wasn't my intention, but it does actually show the correct orientation of how they are mounted, i.e. to the vertical surface of the transom. There will also be two brackets, on for each davit.

[sailah]

I have some Forespar davits but removed and stowed them ashore as I didn't like the look of them on my boat. The bottoms attach to pad eyes on the deck, and the pushpit, and they also are triangulated to another pad eye forward to provide the forward vector with a wire rope. I should think you'd want to rig up something similar to remove the bending moment from the transom. That way the load on the transom is just downward shear and maybe a bit focused forward on the transom. But the bulk of the force trying to flex the transom can be eliminated with some pad eyes on backing plates.

They also have bars that triangulate the forces port and starboard to prevent the davit arms from moving to the side.

No way in the world I would rely on my transom laminate to provide the strength of supporting a RIB cantilevered out.